For perhaps the last time, a researcher
has visited iceberg B-15A, an enormous
fragment of ice that broke away from Antarctica's
Ross Ice Shelf in March 2000.
During a one-hour visit on Jan. 29 (New
Zealand time), Douglas MacAyeal of the
University of Chicago upgraded the software
of an automated weather station on the
enormous piece of ice that helps track
the iceberg's position and reports on
the microclimate of the ice surface.
MacAyeal's work is supported by the National
Science Foundation (NSF) through the U.S.
Antarctic Program.
MacAyeal and other researchers placed weather
stations on the iceberg a year ago. This
year, MacAyeal flew twice to B-15A on
U.S. Coast Guard helicopters to update
the software that allows the weather stations
to transmit data and to adjust the sensors
that measure wind speed.
MacAyeal said that collisions between B-15A
and a much smaller, though still impressive,
iceberg, dubbed C-16, have begun the process
of breaking up the bigger berg. He suspects
B-15A will crumble into pieces and drift
northward away from McMurdo Sound when
summer returns to Antarctica, almost a
year from now.
"B-15A is ripe" for a breakup, he said.
"But it's a 'wait and-see' sort of thing."
During the flights to and from the iceberg
from McMurdo Station, the main NSF research
station in Antarctica, MacAyeal pointed
out enormous cracks developing on the
berg's surface. He also noted areas where
the two icebergs have ground together,
generating as much as 4,000 pounds per
square inch of pressure. A zone between
the two bergs features both narrow ice
canyons 30 meters (100 feet) deep and
spacious bays, in which icebergs that
ordinarily would be thought of as colossal
seem insignificant in comparison with
their larger neighbors. MacAyeal noted
that few human eyes have seen such phenomena.
The collisions, he said, accelerate the
breakup of both bergs and the movement
of the remaining fragments out to sea.
By observing B-15A and C-16, "we've learned
that collisions of this nature provide
a force that helps propel an iceberg on
its track," MacAyeal said.
He added that it is possible that scientists
may be observing for the first time a
cycle in which portions of the Ross Ice
Shelf break off and fall into the sea
as giant icebergs. The National Ice Center,
in Suitland, Md., reported that a new
iceberg, dubbed C-17, broke away from
the Ross Shelf on Feb. 7. C17, which broke
away from the Matusevich Glacier, is estimated
to be 58 square miles in area, or roughly
the size of Manhattan Island.
U.S. Coast Guard pilot Sidonie
Bosin sketches out a proposed
route for an informal photo
reconnaissance of iceberg
B-15.
Photo credit: Peter West/National
Science Foundation
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One of the automated weather
stations on the iceberg.
Photo credit: Peter West/National
Science Foundation
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A U.S. Coast Guard helicopter drops a
smoke marker on the surface of iceberg
B-15A to help determine wind direction
for a landing. Mt. Erebus, almost 13,000
feet high and the world's southernmost
active volcano, is visible in the background.
Photo credit: Peter West/National
Science Foundation
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Douglas MacAyeal, a National Science Foundation-funded
researcher from the University of Chicago,
uploads new instructions to an automated
weather station on iceberg B-15A. MacAyeal
landed on the immense iceberg, perhaps
for the last time, in January to service
weather stations he had placed on the
iceberg a year ago.
Photo credit: Peter West/National
Science Foundation
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Smaller icebergs of varying sizes float
in a zone between iceberg B-15A and a
smaller, but still extremely large berg
designated C-16. The collision zone between
the two bergs is marked by narrow canyons
and wide, ice-choked bays as well as by
areas such as those in the center of the
picture, where the edges of the bergs
have been forced up into peaks by collisions.
Photo credit: Peter West/National
Science Foundation
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One of the many fissures that are forming
within iceberg B-15A, which NSF-funded
researcher Douglas MacAyeal believes will
cause the iceberg to break up and drift
northward. The cracks are perhaps many
hundreds of meters deep.
Photo credit: Peter West/National
Science Foundation
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A U.S. Coast Guard helicopter departs
iceberg B-15.
Photo credit: Peter West/National
Science Foundation
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